Effects of Ca2+Zr4+ ion pairs on spectroscopic properties of Cr3+ multisites in Cr3+-doped Gd3Ga5O12 garnets

Abstract
Some disorder exists in Gd3Ga5O12 (GGG) garnets because of a partial occupation of the octahedral sites by the Gd3+ ions. The luminescence of the Cr3+ ions introduced as dopant in the material is then affected. The situation is worse in (Ca,Zr)‐substituted GGG due to a great deal of Ca‐Zr defects introduced in large quantity in order to have a congruent composition. A simple model based on the local dilatation of the lattice around each defect is presented in order to describe the Cr3+ luminescence at any temperature. The influence of Ca‐Zr ion pairs on the average Cr3+→Tm3+ energy transfer is also studied.